Labour productivity has gone up (As has labour participation, if you compare it to the 50s and 60s). It should more than counterbalance a demographic-caused dip in labour participation rates. Fewer people, working less, produce more today than they did 40 years ago.
We produce more for less work. Why can't that be turned into a lower labour participation rate, while maintaining the same quality of life, despite demographic shifts?
Yes I read your post it was like half a paragraph…We produce more but there’s more retirees and they live longer.
At the end of the day the contributors have to siphon off part of their earnings to give to the beneficiaries. Believe it or not, there is in fact many scenarios where the entitlements of the beneficiaries exceeds the input from the contributors. Just because we produce more per worker, does not mean we can support any arbitrary ratio of workers to retirees (who become more expensive over time).
Social security-like systems require a growing population to sustain.